The invention concerns digital radiology, notably digital mammography and, in particular, the automatic detection of a graduated compression paddle of a mammography apparatus.
In mammography, a compression paddle is a support making it possible to receive under compression the breast of the person to be observed. A compression paddle includes a graduation appearing on two perpendicular sides of a rectangular opening in the compression surface.
As is standard, in radiology, the exposure parameters such as the focal path chosen (in the case of a device with double focal path), the filter used, the voltage applied to the tube (kV), the presence or absence of grid, the contact magnification and the product of the anode current by the exposure time (m A.s), constituting what is called the configuration, are initially determined from a user's choice for the parameters of grid presence or absence, magnification or contact and a table of automatic optimization of parameters (AOP), as function of the user's choice, for the parameters kV, focal path, filter and m A.s. The organ part examined then undergoes a pre-exposure with a low m A.s value in order to determine the characteristics of the organ part examined, particularly the equivalent radiological thickness, and the exposure parameters are then adjusted from those characteristics. The mode of automatic acquisition known as AOP is disclosed in EP-0,402,244, EP-0,465,360 and FR-2,786,389.
In an AOP automatic mode, optimization of the parameters of the tube is a function of the most glandular area of the breast. The most glandular area of the breast is expressed as being the lowest brightness level observed on a cell in the order of 1 cm2 in the pre-exposure image. The plumb marks of graduation of the compression paddle, combined with the thickness of the region of the breast under the marks, contribute to weakening the signal in the image. Consequently, the effects of attenuation of the marks can cause a poor detection of the most glandular area of the breast. In fact, the combination of the marks and of the area of the breast situated under those marks produces a greater attenuation than that of the most glandular area of the breast. The parameters of the tube are, consequently, optimized on that combination of “marks and breast area,” situated under the marks, rather than on the most glandular area of the breast.
Further, the use of parameters of the tube not optimized can lead to irregular X-ray doses, which may affect image quality.